De-worming Your Dog

De-worming Dogs

By isak, September 18, 2015

Ever wonder which wormer kills what worm? If you know what specific parasite is affecting your dogs, you don’t need to spend the money on a broad spectrum dewormer when a specific anthelmintic will suffice. Why attack something that isn’t there?

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Interceptor, unlike any of the Droncit, Drontal, Drontal Plus anthelmintics does NOT kill tapeworms of any kind. For that, you need praziquantel (or fenbendazole for the Taeniid-type tapeworms).

Aside from tapeworms, there are other differences (think lawyerly weasle words) if you read the label carefully. I recall that Interceptor (milbemycin oxime) “prevents” heartworm, “kills” hookworms, and “controls” round worms and whipworms. And, that verbage can change over time with added research.

The different wordings relate to whether or not a specific dewormer kills only adults in the intestine, and/or migrating larvae in the tissues, as well as how infective and resistant the environmental forms are.

I believe milbemycin oxime does kill migrating hookworm larvae in the tissues. In addition to which, hookworm larvae in the environment are very fragile and easily removed, believe it or not. Hence, Interceptor can claim to kill hooks.

On the other hand, ascarid and whip worm eggs are tough as nails and almost can’t be killed in the environment. In addition to which, whip worms take two to three months to develop, unlike the hooks and ascarids, which take three weeks. Thus, most people stop treating for whips way too soon. Whips don’t have a tissue-migration stage, so if you treat only once with Interceptor, you won’t kill all the whips because of the juveniles developing in the intestine over two months. If you give it every month, though, it should be good enough.

I’m not sure milbemycin oxime is very effective against the migrating ascarid larvae in the tissues, coupled with the fact the the juveniles become adults in three weeks, not a month. So, if you treat only once, or once every month, you will be missing a few ascarids which will be adults in the intestines at three weeks, making more eggs for a week before the next monthly treatment. Hence the term “control,” which is not the same as kill.

Studies also have shown that milbemycin oxime is not quite as effective in killing either ascarids or hookworms as ivermectin, (at the higher dose lethal to p-glyprotein deficient collie types) or to pyrantel or fenbendazole.

However, pyrantel only kills adult ascarids, so you have to retreat in three weeks. Fenbendazole is only effective in killing migrating larvae if you give it day after day and then only in pregnant bitches. Ivermectin, at the low, Heartguard dose, is not effective against ascarids at all. But, at the high, potentially lethal dose, it’s the best choice. Milbemycin falls in the middle because it is safer than high dose ivermectin but not as effective. Not as effective killing adult ascarids as pyrantel, but does kill at least some of the juveniles. It only has to be given once, instead of three days in a row like fendendazole, but, by giving it once a month, instead of every two to three weeks, leaves a window open.

If this stuff was simple you wouldn’t need to go to vet school!! You could find in inside a matchbook cover.

Therefore, as I said before, “What parasite are you trying to kill?”

The cost of the drug is the least important parameter.

If you’re after tapeworms, you have to use a Droncit-type drug (or Panacur or SafeGuard for “Taeniid” tapeworms only). But, you only have to give it once (AND treat for fleas or lice; or stop feeding mice and bunnies or moose and lemmings to the dogs.)

If you’re after whipworms, use a fenbendazole-type. BUT, you have to treat again two and three MONTHS later and scoop, scoop, scoop.

Droncit (praziquantel) kills tapeworms.

Drontal (praziquantel and pyrantel) kills tapeworms, ascarids (“round” worms), and hook worms.

Drontal Plus (praziquantel, pyrantel, and fenbendazole) kills tapeworms, ascarids (“round” worms), hook worms, and whip worms.

It’s all marketing strategies.

More basics:

If you give only a benzimidazole (fenbendazole, febantel, etc.), like Panacur, it will kill whip worms in one day, but hook worms and ascarids take three days of treatments. So, if you treat with Panacur, you have to give it three days in a row, unless you are absolutely, positively positive that you’re only treating whip worms.

Pyrantel, like Strongid and Nemex, kills only hooks and ascarids in one day, so you only have to give it once. It does not kill whips.

So, by combining pyrantel (in Drontal) with fenbendazole (in Drontal Plus) you only have to treat once, not three days in a row, because the pyrantel kills the hooks and rounds in one day and the fenbendazole kills the whips in one day. (The praziquantel kills the tapes in one day in all three products, regardless.)

Now things get confusing, but fascinating:

Drontal Plus is a great marketing tool designed to keep the dewormer competitive by being “broad spectrum.”

Drontal (praziquantal and pyrantel) was the upgrade of simple Droncit (praziquantel only) years ago to compete with Vercom Paste, which was the first major “broad-spoectrum” anthelmintic. Vercom contained praziquantal (tapes) and febantel (ascarids, hooks, and whips). Febantel gets turned into fenbendazole and oxfendazole by the liver.

The problem with Vercom Paste was that you still had to give it three days in a row, like Panacur, to kill the ascarids and rounds. But, it got ALL the tapes, not just the mammallian tapes (Taenia) that Panacur got. (Panacur doesn’t kill flea tapeworms).

Vercom was broader spectrum than either Droncit or Panacur, but it still had to be given three days in a row (and it tasted just awful — cats would get mad as hell when treated, especially by day three!!)

So Droncit, by adding pyrantel, could be marketed as a one-day dewormer that killed all types of tapes, plus ascarids and rounds. Unfortunately, it didn’t kill whips. Panacur and Vercom did (but had to be given over three days). The world was not yet perfect.

So Drontal added in fenbendazole initially (instead of febantel, I suppose because of patent laws held by Vercom?). It was called Drontal Plus. Ingenious marketing. Now you could give one pill just one day for tapes, ascarids, rounds, and whips! They nailed the broad spectrum market and blasted the three-day-in-a-row Vercom Paste and Panacur.

Things get even murkier (God bless American free enterprise):

Febantel must not be protected any longer because now Drontal Plus uses it instead of fenbendazole. In addition, pyrantel tartrate is absorbed by the intestines faster than pyrantel pamoate, so many products that used to include the p-pamoate now use p-tartrate.

It gets better:

Even newer is pyrantel emboate, which apparently requires half the dose of the pamoate. AND, Oxantel pamoate got invented, to kill human whip worms, even though its close cousins pyrantel pamoate and p-tartrate don’t. Now oxantel is used for canine whips, as well.

These advances have allowed other companies to capitalize on the “broad spectrum” market. Now you can find an “allwormer” with praziquantel, pyrantel emboate, febantel, and/or oxantel, all mixed up in some combination and licensed for tapes, ascarids, hooks, and whips, and all in a one-day treatment.

I suspect Drontal Plus still uses the pyrantel emboate AND good old febantel because it works as well or better than oxantel, OR because they can’t get the license because of patent infringment. That may change when the patent expires.

Therefore, I would use either the Drontal Plus, with febantel, or the Allwormer, with the oxantel at this time because I can’t find the actual published studies reporting the laboratory effectiveness of febantel against oxantel for whips. Otherwise, the products are the same, in that praziquantel is praziquantel and pyrantel is pyrantel, even though the latter can be absorbed at different rates depending on which analog is used (pamoate, tartrate, emboate). So, read the label.

Oh yes, it gets even better!! Now there’s Drontal for Puppies! This product doesn’t include praziquantel because of the life cycle of tapeworms — young puppies can’t develop them to adulthood that fast. Drontal for puppies is actually Drontal Plus without the praziquantel (Drontal Minus?? – naw, bad marketing). It contains only febantel and pyrantel embonate for ascarids, hooks, and whips.

With Drontal for Puppies, then, you can treat the same way as if you were using Strongid, except you also are killing whips. However, whips are not a problem in very young puppies. Strongid is good enough.

Broad-spectrum marketing doesn’t end here. Heartguard Plus, Interceptor, Sentinel, and Revolution, all employ some facet of the “kill ’em all” anthelmintic strategy now.

Ah, commerce and industry! One spends the first half of one’s veterinary career trying to figure out how a product works and the last half trying to figure out why products get invented in the first place.

Oh yes, money.

Print this out, study it, memorize it, then impress the hell out of your local veterinarian!!

And remember, we don’t give worms to dogs, we de-worm them, which alone is reason enough why I never prescribe “Allwormer.” Drives me absolutely nuts!!

Finally, if you know what specific parasite is affecting your dogs, you don’t need to spend the money on a broad spectrum dewormer when a specific anthelmintic will suffice. Why attack something that isn’t there? After all, worms aren’t weapons of mass destruction.

Good luck and wait a couple of years. This will all change again.

SourceDr. Jerry Vanek


  1. Allie says:

    My dog had tapeworms about three weeks ago and we used safeguard which seemed to clear them up.. today I noticed another WORM! We live in North Dakota and right now it’s below zero everyday.. could he be getting them from eating other dogs waste?

    Can I re treat with de wormer again ?

    • isak says:

      The tapeworms can lay eggs that will not hatch for about four weeks. So, yes, you can de-worm your dog again. It is generally recommended to de-worm twice four weeks apart just for this reason. You also need to be sure he is flea-free, too.

  2. Kate says:

    So very informative. Thank you for explaning a complicated problem simply.

  3. Holly Sellers says:

    Thank you so much for all the helpful info on DE-worming products!

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